In many environments where high amounts of dust or other contaminants are airborne, fibrous filtration face masks are commonly used to protect workers. The masks remove particulate material from the air before it is inhaled by the mask wearer. In some environments, the mask is used to protect neighboring persons, that is, those other than the mask wearer, or nearby objects, such as devices being constructed in a clean room. The protection of neighboring persons and nearby objects is afforded by removing infectious contaminants from air exhaled by the mask wearer.
Fibrous filtration face masks generally have a porous mask body that is shaped and adapted to filter the inhaled or exhaled air. Air passes through the mask material, but a filter layer in the mask removes particulates within the air stream to provide clean air for inhalation by the wearer. Similarly, exhaled air passes through the mask material, but pathogens and other contaminants are retained by the mask so that they cannot contaminate the surrounding environment.
Fibrous filtration face masks that pass National Institute for Occupational Safety and Health (NIOSH) standards for purity of inhaled air are often called respirators (see 42 C.F.R. 84 (1995)). Respirators are commonly worn to protect the wearer when the ambient air contains toxic, noxious, or other harmful materials. Under such circumstances, the respirator must not only filter the harmful substances from the air stream, but it must also fit tightly against the face of the wearer to prevent contaminants from leaking around the edge of the respirator and into the breathing zone of the wearer.
Filtering face masks exist with many various shapes and features. The filtering face mask may be a molded or formed cup-shaped mask, that is intended to securely cover the nose and mouth of the wearer. Some filtering face masks, such as surgical face masks, are essentially flat. An exhalation valve, which opens under increased internal air pressure, for example, when the wearer exhales, may be included on a filtering face mask. See, for example, U.S. Pat. No. 4,827,924 to Japuntich. Masks with exhalation valves are typically used when the underlying purpose of the mask is to remove particulates from the air to be inhaled. Other features on face masks include nose clips that may improve the fit over the wearer's nose and where the nose meets the cheeks. See U.S. Pat. No. 5,558,089 to Castiglione.
Head bands are also commonly used on masks. The bands are used to position the mask snugly over the wearer's nose and mouth. The bands are often an elastic tape or thin film attached to the edges of the mask body by mechanical systems such as staples. Other mechanical fastening systems such as stitching, snaps, and buckles are used to attach the bands to the mask body. The use of an adhesive to attach the bands is also known, as is high frequency heat bonding of bands to the mask body. See, for example, U.S. Pat. Nos. 4,802,473 and 4,941,470 to Hubbard et al.
Staples are a very common system for attaching the bands to the mask body because staples are quick and easy to install, and are fairly inexpensive. Although staples are regularly used for this purpose, there are some disadvantages associated with them. One disadvantage is that the staples are typically made from a metal, which is highly conductive and therefore quickly heats up or chills. This characteristic can cause discomfort for the mask wearer at points where the metal contacts the wearer's skin.
In some industries, staples or other mechanical fasteners are not recommended. For example, in the food industry, some locations restrict the use of face masks with staples. The rationale is that the staples could, theoretically, be removed from the mask and contaminate a food product. Thus, on face masks used in the food industry, the bands are typically attached to the mask body with an adhesive, are sewn on, or are attached by ultrasonic welding.
Attempts have been made to eliminate the use of staples and other removable mechanical fasteners by attaching the bands to the mask body through ultrasonic welding. Elastic bands that are a tape or film of elastic material have been attached to mask bodies by this method. The bands that have been attached by welding have difficulty withstand in high temperature environments because the bands are generally made from a thermoplastic elastomer. Polyester and elastic braided and knitted bands have also been attached to mask bodies by ultrasonic welding. The temperatures needed to obtain an adequate bond between the polyester in the band and a layer of the mask body are typically sufficiently high to melt layers of the mask body. The needed heating temperatures, however, may be so high that holes are melted through the thickness of the mask in the proximity of the welded area. This leads to a narrow processing window. That is, the temperature range that will provide an adequate bond is small and therefore, processing condition tolerances need to be tightly controlled when attempting to weld polyester materials. A variation either way may not provide an adequate bond or may excessively melt the mask body, resulting in holes or thin spots through the mask body. Stress from stretching the headband may enlarge the holes or cause thin spots to become holes. Such holes may allow particulates and other debris to contaminate the inhaled air stream.
Attempts also have been made to weld elastic bands to other headgear-type articles, such as a plastic face shield. See, for example, U.S. Pat. No. 5,440,760 to Highsmith. A face shield is a transparent, liquid-impermeable shield that covers the wearer's face and protects it from flying particulates and liquid spray but does not filter the air inhaled or exhaled by the user. The positioning of a face shield on a wearer's face is not as critical as the positioning of a filtering face mask.
Face shields are generally rigid and made from a light-weight material, such as polyester, polycarbonate, and the like. Highsmith discloses using a heat-bondable elastic material, which can be an elastic material surrounded by a heat-bondable cover or carrier, as a band to support a face shield on a wearer's head. This heat-bondable cover or carrier is disclosed as being polyester, polypropylene, nylon, or any combination thereof As mentioned above, face shields protect the wearer from large flying objects, and avoiding pin holes in face shields is not as critical as it is for filtering face masks. Face shields are able to tolerate band and weld imperfections, such as small pin holes melted into the shield which would not be acceptable in a filtering face mask or respirator.